The present invention relates to a tubular stent/graft apparatus. More particularly, the present invention relates to a composite intraluminal device including a helically formed tubular stent/graft assembly formed from a planar pre-assembly having a wire stent material laminated between ePTFE strips.
An intraluminal prosthesis is a medical device commonly known to be used in the treatment of diseased blood vessels. An intraluminal prosthesis is typically used to repair, replace, or otherwise correct a damaged blood vessel. An artery or vein may be diseased in a variety of different ways. The prosthesis may therefore be used to prevent or treat a wide variety of defects such as stenosis of the vessel, thrombosis, occlusion, or an aneurysm.
One type of endoluminal prosthesis used in the repair of diseases in various body vessels is a stent. A stent is a generally longitudinal tubular device formed of biocompatible material which is useful to open and support various lumens in the body. For example, stents may used in the vascular system, urogenital tract and bile duct, as well as in a variety of other applications in the body. Endovascular stents have become widely used for the treatment of stenosis, strictures, and aneurysms in various blood vessels. These devices are implanted within the vessel to open and/or reinforce collapsing or partially occluded sections of the vessel.
Stents are generally open ended and are radially expandable between a generally unexpended insertion diameter and an expanded implantation diameter which is greater than the unexpended insertion diameter. Stents are often flexible in configuration, which allows them to be inserted through and conform to tortuous pathways in the blood vessel. The stent is generally inserted in a radially compressed state and expanded either through a self-expanding mechanism, or through the use of balloon catheters.
A graft is another type of commonly known type of intraluminal prosthesis which is used to repair and replace various body vessels. A graft provides an artificial lumen through which blood may flow. Grafts are tubular devices which may be formed of a variety of material, including textiles, and non-textile materials. One type of non-textile material particularly useful as an implantable intraluminal prosthesis is polytetrafluoroethylene (PTFE). PTFE exhibits superior biocompatability and low thrombogenicity, which makes it particularly useful as vascular graft material in the repair or replacement of blood vessels. In vascular applications, the grafts are manufactured from expanded polytetrafluoroethylene (ePTFE) tubes. Such tubular grafts may be formed from extruded tubes, sheets or films. These tubes have a microporous structure which allows natural tissue ingrowth and cell endothelization once implanted in the vascular system. This contributes to long term healing and patency of the graft.
Grafts formed of ePTFE have a fibrous state which is defined by interspaced nodes interconnected by elongated fibrils. The spaces between the node surfaces that is spanned by the fibrils is defined as the internodal distance (IND). Porosity of a graft is measured generally by IND. In order of proper tissue ingrowth and cell endothelization, grafts must have sufficient porosity obtained through expansion. When the term expanded is used to describe PTFE, it is intended to describe PTFE which has been stretched, in accordance with techniques which increase IND and concomitantly porosity. The stretching may be in uni-axially, bi-axially, or multi-axially. The nodes are spaced apart by the stretched fibrils in the direction of the expansion. Properties such as tensile strength, tear strength and radial (hoop) strength are all dependent on the expansion process. Expanding the film by stretching it in two directions that are substantially perpendicular to each other, for example longitudinally and transversely, creates a biaxially oriented material. Films having multi-axially-oriented fibrils may also be made by expanding the film in more than two directions. Porous ePTFE grafts have their greatest strength in directions parallel to the orientation of their fibrils. With the increased strength, however, often comes reduced flexibility.
While ePTFE has been described above as having desirable biocompatability qualities, tubes comprised of ePTFE, as well as films made into tubes, tend to exhibit axial stiffness, and minimal radial compliance. Longitudinal compliance is of particular importance to intraluminal prosthesis as the device must be delivered through tortuous pathways of a blood vessel to the implantation site where it is expanded. A reduction in axial and radial flexibility makes intraluminal delivery more difficult.
Composite intraluminal prosthesis are known in the art. In particular, it is known to combine a stent and a graft to form a composite medical device. Such composite medical devices provide additional support for blood flow through weakened sections of a blood vessel. In endovascular applications the use of a composite graft or a stent/graft combination is becoming increasingly important because the combination not only effectively allows the passage of blood therethrough, but also ensures patency of the implant.
However, in each of the above described sheet or film cases, the stent and the graft are separately formed and then attached. This manner of construction results in potential separation of the graft from the stent because it is difficult to affix tubular structures to one and another.
The present invention seeks to provide a more efficient and predictable means of forming a stent/graft assembly by forming the tubular covering and tubular stent simultaneously.
It is an object of the present invention to provide an improved composite stent/graft apparatus.
It is a further object of the present invention to provide tubular stent/graft devices that can be manufactured by continuous techniques.
It is a further object of the present invention to produce the assembly strips in a continuous manufacturing technique to reduce the cost of manufacturing the tubular stent/grafts.
It is still a further object of the present invention to provide a tubular stent/graft that has consistent wall properties without undesired seams, bumps or weak points.
In the efficient attainment of these and other objects, the present invention provides a tubular stent/graft apparatus comprising a planar graft material having a planar stent wire attached to one of its sides to form a strip assembly. The strip assembly is helically wound to form a tubular stent/graft structure.
The stent may be radially expandable, and the stent may be chosen from a wide variety of stent materials and configurations. For example, the stent may be self-expandable, balloon expandable or made from a memory alloy, the configuration of which can be controlled by temperature.
The present invention further relates to a method of making a tubular stent/graft assembly comprising the steps of (i) forming a substantially planar strip and wire assembly comprising planar graft material formable into a graft and planar stent wire formable into a radially adjustable stent, wherein the wire is attached lengthwise along the length of said planar strip; and (ii) helically winding the substantially planar strip and wire assembly to form said tubular stent graft assembly.